[CORE] vmm_guest_aspace: Fix is_region_overlapping() for adjacent regions

If we have two regions A and B adjacent to each other in guest physical
address space then is_region_overlapping() will fail if device tree node
for region B is before region A under guest aspace node.

This patch fixes above described issue in is_region_overlapping().

Signed-off-by: Anup Patel <anup@brainfault.org>